N-zno/n-gan/n-zno heterojunction-based bidirectional ultraviolet light-emitting diode and preparation method therefor

ABSTRACT

The present invention discloses a bidirectional ultraviolet light emitting diode (UV LED) based on N—ZnO/N—GaN/N—ZnO heterojunction as well as its preparation method. The LED includes: N—ZnO microwires, a N—GaN film, a PMMA protective layer and alloy electrodes; and its preparation method includes the following steps: lay two N—ZnO microwires on the N—GaN film, then spin-coat a PMMA protective layer on the film to fix the N—ZnO microwires until the PMMA protective layer spreads over the N—ZnO microwires, and then place the film on a drying table to solidify the PMMA protective layer; then etch the PMMA protective layer with O2 to expose the N—ZnO microwires, and prepare alloy electrodes on different N—ZnO microwires to construct a N—ZnO/N—GaN/N—ZnO heterojunction to constitute a complete device. The present invention constructs an N/N/N symmetrical structure; the device is composed of N—ZnO and N—GaN, emits light in the ultraviolet region and has a small turn-on voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Section 371 National Stage Application No.PCT/CN2019/089066, filed on May 29, 2019, and claims priority to ChinesePatent Application No. 2019103388046.7, filed on Apr. 25, 2019, thecontents of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to the technical field of semiconductoroptoelectronic devices, especially a bidirectional ultraviolet lightemitting diode (UV LED) based on N—ZnO/N—GaN/N—ZnO heterojunction aswell as its preparation method.

BACKGROUND TECHNOLOGY

Zinc oxide has a high exciton binding energy of 60 meV and a wide directband gap of 3.37 eV. It is a very promising semiconductor material forUV LED, especially laser LED. The p-type doped zinc oxide technology hasdeveloped rapidly in recent years, but there are still many difficultiesin obtaining highly stable p-type zinc oxide. This hinders thedevelopment of zinc oxide-based UV LED and laser LED. In order to solvethis problem, P—GaN is introduced to prepare zinc oxide-based UV LED andlaser LED, but it still has many problems, such as low carrierconcentration and high square resistance. In addition, the electricallypumped excitation spectrum of the N—ZnO/P—GaN heterojunction structureis mostly the visible light emission (−420 nm) related to defects inP—GaN, and the ultraviolet emission in N—ZnO is always suppressed. Fromthe perspective of process and quality (carrier concentration, carriermobility, square resistance), N—GaN outperforms P—GaN, and itspreparation process is simple.

The traditional lighting drive circuit is composed of a power factorcorrection circuit, an AC/DC converter circuit and an output constantcurrent circuit. If bidirectional LED is used, only two circuits may beneeded. However, the existing bidirectional LED structure has differentemission wavelengths and different light intensities under forward biasand reverse bias. The light intensity and wavelength of the LED are thetwo main factors that affect strobe light, which is harmful to the eyes.Therefore, bidirectional LED now has few applications in the fields oflighting and display.

SUMMARY OF THE INVENTION

The solution provided by the present invention to the above technicalproblem is to provide a bidirectional UV LED based on N—ZnO/N—GaN/N—ZnOheterojunction as well as its preparation method. The present inventionuses N—ZnO and N—GaN to construct a symmetrical structure, which has ahigh proportion of ultraviolet light emission, a low turn-on voltage, anunchanged total amount of light emitted under the forward and reversebias and a little change in light emission wavelength. Such a structurecan be used to prepare bidirectional LED for lighting and displayapplications.

To solve the above technical problem, the present invention provides abidirectional UV LED based on N—ZnO/N—GaN/N—ZnO heterojunction,including: N—ZnO microwires, a N—GaN film, a PMMA protective layer andalloy electrodes; two N—ZnO microwires are laid on the N—GaN film, and aPMMA protective layer is then spin-coated on the film to fix the N—ZnOmicrowires, and alloy electrodes are prepared on different N—ZnOmicrowires, respectively.

Preferably, the electron concentration of the N—ZnO micronwires is10¹⁶-1 0¹⁹/cm³, and their electron mobility is 5-40 cm⁻²C/V.s.

Preferably, the N—GaN film is 0.5-10 μm thick, its electronconcentration is 10¹⁷-10¹⁹/cm³, and its electron mobility is 20-100cm²/V.s.

Preferably, the electrodes are all located on the N—ZnO microwires andare Ni/Au alloy electrodes or Ti/Au alloy electrodes.

Correspondingly, the preparation method of a bidirectional UV LED basedon N—ZnO/N—GaN/N—ZnO heterojunction includes the following steps:

-   -   (1) Mix and grind ZnO powder having a purity of 99.97-99.99% and        500 nm-2,000 nm carbon powder in a mass ratio of 1:1-1:1.3, and        then fill the mixture into a ceramic boat; cut the silicon slice        substrate into 3.2 cm×3 cm slices, then ultrasonically clean the        silicon slices with a mixed solution of acetone and absolute        ethanol and then dry them with nitrogen. Used as a type of        growth substrate, the silicon slices are placed in a quartz tube        having a length of 20 cm and a diameter of 8 cm with openings at        both ends. The cleaned sapphire slice substrate is also placed        in the quartz tube and is 10 cm away from the mouth of the tube.        The entire quartz tube is pushed horizontally into a tube        furnace for high temperature reaction and is infused with 150        sccm argon gas and 15 sccm oxygen gas; the substrate is composed        of silicon slices or sapphire slices:    -   (2) After the reaction, the N—GaN substrate is ultrasonically        cleaned with acetone, absolute ethanol and deionized water in        sequence and then dried with nitrogen;    -   (3) Pick out two N—ZnO microwires from the reactant in Step (1),        lay the two N—ZnO microwires on the N—GaN film, then spin-coat a        PMMA protective layer on the film to fix the N—ZnO microwires        until the PMMA protective layer spreads over the N—ZnO        microwires, and then place the film on a drying table to        solidify the PMMA protective layer; then etch the PMMA        protective layer with O₂ to expose the N—ZnO microwires, and        prepare alloy electrodes on different N—ZnO microwires,        respectively;    -   (4) Measure the electrical properties of the N—ZnO/N—GaN/N—ZnO        heterojunction-based LED finally produced in Step (3), and        measure its electrically pumped luminescence spectrum.

Preferably, in Step (1), the temperature for high-temperature reactionis 1,000-1,100° C., and the reaction time is 90-180 minutes.

Preferably, in Step (3), the metal plating method is magnetronsputtering, thermal evaporation or electron beam evaporation, and theplating thickness is 20-60 nm.

The beneficial effects of the present invention are: (1) Make use ofN—ZnO microwires and N—GaN film to construct LED, which has a highproportion of ultraviolet light emission and a low turn-on voltage; (2)The device has a symmetrical structure, emits the same amount of lightunder forward and reverse bias, has a little change in the luminouswavelength and can be used in lighting and display fields; (3) Thelight-emitting positions of the N—ZnO/N—GaN/N—ZnO heterojunction-basedLED provided by the present invention are 371 nm and 385 nm, theultraviolet luminescence accounts for more than 80% of the totalluminescence of the LED, and the device can work normally under ACdrive.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 shows a scanning electron microscope image of the N—ZnO microrodsynthesized in Embodiment case 1 of the present invention after etching.

FIG. 2 shows a schematic diagram of the structure of N—ZnO/N—GaN/N—ZnOheterojunction-based LED provided by the present invention.

FIG. 3 shows the electroluminescence (EL) spectra of theN—ZnO/N—GaN/N—ZnO heterojunction-based LED synthesized in Embodimentcase 1 of the present invention under different injection AC voltages atroom temperature.

EMBODIMENTS

As shown in FIG. 1 and FIG. 2, a bidirectional UV LED based onN—ZnO/N—GaN/N—ZnO heterojunction, including: N—ZnO microwires, a N—GaNfilm, a PMMA protective layer and alloy electrodes; two N—ZnO microwiresare laid on the N—GaN film, and a PMMA protective layer is thenspin-coated on the film to fix the N—ZnO microwires, and alloyelectrodes are prepared on different N—ZnO microwires, respectively.

The electron concentration of the N—ZnO micronwires is 10¹⁶-10¹⁹/cm³,and their electron mobility is 5-40 cm²/V.s. The N—GaN film is 0.5-10 μmthick, its electron concentration is 10¹⁷-10¹⁹/cm³, and its electronmobility is 20-100 cm²/V.s. The electrodes are all located on the N—ZnOmicrowires and are Ni/Au alloy electrodes or Ti/Au alloy electrodes.

Correspondingly, the preparation method of a bidirectional UV LED basedon N—ZnO/N—GaN/N—ZnO heterojunction includes the following steps:

-   -   (1) Mix and grind ZnO powder having a purity of 99.97-99.99% and        500 nm-2,000 nm carbon powder in a mass ratio of 1:1-1:1.3, and        then fill the mixture into a ceramic boat; cut the silicon slice        substrate into 3.2 cm×3 cm slices, then ultrasonically clean the        silicon slices with a mixed solution of acetone and absolute        ethanol and then dry them with nitrogen. Used as a type of        growth substrate, the silicon slices are placed in a quartz tube        having a length of 20 cm and a diameter of 8 cm with openings at        both ends. The cleaned sapphire slice substrate is also placed        in the quartz tube and is 10 cm away from the mouth of the tube.        The entire quartz tube is pushed horizontally into a tube        furnace for high temperature reaction and is infused with 150        sccm argon gas and 15 sccm oxygen gas.    -   (2) After the reaction, the N—GaN substrate is ultrasonically        cleaned with acetone, absolute ethanol and deionized water in        sequence and then dried with nitrogen;    -   (3) Pick out two N—ZnO microwires from the reactant in Step (1),        lay the two N—ZnO microwires on the N—GaN film, then spin-coat a        PMMA protective layer on the film to fix the N—ZnO microwires        until the PMMA protective layer spreads over the N—ZnO        microwires, and then place the film on a drying table to        solidify the PMMA protective layer; then etch the PMMA        protective layer with O₂ to expose the N—ZnO microwires, and        prepare alloy electrodes on different N—ZnO microwires,        respectively;    -   (4) Measure the electrical properties of the N—ZnO/N—GaN/N—ZnO        heterojunction-based LED finally produced in Step (3), and        measure its electrically pumped luminescence spectrum.

In Step (1), the temperature for high-temperature reaction is1,000-1,100° C., and the reaction time is 90-180 minutes. In Step (3),the metal plating method is magnetron sputtering, thermal evaporation orelectron beam evaporation, and the plating thickness is 20-60 nm.

Embodiment case 1:

-   -   (1) Mix and grind ZnO powder having a purity of 99.99% and 500        nm-2,000 nm carbon powder in a mass ratio of 1:1, and then fill        the mixture into a ceramic boat; cut the silicon slice substrate        into 3.2 cm×3 cm slices, then ultrasonically clean the silicon        slices with a mixed solution of acetone and absolute ethanol and        then dry them with nitrogen. Used as a type of growth substrate,        the silicon slices are placed in a quartz tube having a length        of 20 cm and a diameter of 8 cm with openings at both ends. The        cleaned sapphire slice substrate is also placed in the quartz        tube and is 10 cm away from the mouth of the tube. The entire        quartz tube is pushed horizontally into a tube furnace for high        temperature reaction and is infused with 150 sccm argon gas and        15 sccm oxygen gas.    -   (2) After the reaction, the N—GaN substrate is ultrasonically        cleaned with acetone, absolute ethanol and deionized water in        sequence and then dried with nitrogen;    -   (3) Pick out two N—ZnO microwires from the reactant in Step (1),        lay the two N—ZnO microwires on the N—GaN film, then spin-coat a        PMMA protective layer on the film to fix the N—ZnO microwires        until the PMMA protective layer spreads over the N—ZnO        microwires, and then place the film on a drying table to        solidify the PMMA protective layer; then etch the PMMA        protective layer with O₂ to expose the N—ZnO microwires, and        prepare alloy electrodes on different N—ZnO microwires,        respectively;    -   (4) Measure the electrical properties of the N—ZnO/N—GaN/N—ZnO        heterojunction-based LED finally produced in Step (3), and        measure its electrically pumped luminescence spectrum. Under        different voltages at 100 Hz, the light-emitting positions of        the LED are 371 nm and 385 nm, and the ultraviolet luminescence        accounts for more than 85% of the total luminescence of the LED.

In Step (1), the temperature for high-temperature reaction is1,000-1,100° C., and the above-mentioned reaction time is 120 minutes.In Step (3), the metal plating method is magnetron sputtering, thermalevaporation or electron beam evaporation, and the plating thickness is45 nm.

FIG. 3 shows the electrically pumped luminescence spectrum of theN—ZnO/N—GaN/N—ZnO heterojunction-based LED synthesized in Embodimentcase 1 under different AC voltages. The light-emitting positions of theLED are located at 371 nm and 385 nm and do not change with voltage.

1. A bidirectional ultraviolet light emitting diode (UV LED) based onN—ZnO/N—GaN/N—ZnO heterojunction is characterized by: it includes: N—ZnOmicrowires, a N—GaN film, a PMMA protective layer and alloy electrodes;two N—ZnO microwires are laid on the N—GaN film, and a PMMA protectivelayer is then spin-coated on the film to fix the N—ZnO microwires, andalloy electrodes are prepared on different N—ZnO microwires,respectively; the electron concentration of the N—ZnO micronwires is10¹⁶-10¹⁹/cm³, and their electron mobility is 5-40 cm²/V.s. 2.(canceled)
 3. A bidirectional UV LED based on N—ZnO/N—GaN/N—ZnOheterojunction described in claim 1 is characterized by: the N—GaN filmis 0.5-10 μm thick, its electron concentration is 10¹⁷-10¹⁹/cm³, and itselectron mobility is 20-100 cm²/V.s.
 4. A bidirectional UV LED based onN—ZnO/N—GaN/N—ZnO heterojunction described in claim 1 is characterizedby: the electrodes are all located on the N—ZnO microwires and are Ni/Aualloy electrodes or Ti/Au alloy electrodes.
 5. The preparation method ofa bidirectional UV LED based on N—ZnO/N—GaN/N—ZnO heterojunction ischaracterized by: it includes the following steps: (1) Mix and grind ZnOpowder having a purity of 99.97-99.99% and 500 nm-2,000 nm carbon powderin a mass ratio of 1:1-1:1.3, and then fill the mixture into a ceramicboat; cut the silicon slice substrate into 3.2 cm×3 cm slices, thenultrasonically clean the silicon slices with a mixed solution of acetoneand absolute ethanol and then dry them with nitrogen. Used as a type ofgrowth substrate, the silicon slices are placed in a quartz tube havinga length of 20 cm and a diameter of 8 cm with openings at both ends. Thecleaned sapphire slice substrate is also placed in the quartz tube andis 10 cm away from the mouth of the tube. The entire quartz tube ispushed horizontally into a tube furnace for high temperature reactionand is infused with 150 sccm argon gas and 15 sccm oxygen gas; thesubstrate is composed of silicon slices or sapphire slices; (2) Afterthe reaction, the N—GaN substrate is ultrasonically cleaned withacetone, absolute ethanol and deionized water in sequence and then driedwith nitrogen; (3) Pick out two N—ZnO microwires from the reactant inStep (1), lay the two N—ZnO microwires on the N—GaN film, then spin-coata PMMA protective layer on the film to fix the N—ZnO microwires untilthe PMMA protective layer spreads over the N—ZnO microwires, and thenplace the film on a drying table to solidify the PMMA protective layer;then etch the PMMA protective layer with O₂ to expose the N—ZnOmicrowires, and prepare alloy electrodes on different N—ZnO microwires,respectively; (4) Measure the electrical properties of theN—ZnO/N—GaN/N—ZnO heterojunction-based LED finally produced in Step (3),and measure its electrically pumped luminescence spectrum.
 6. Thepreparation method of a bidirectional UV LED based on N—ZnON—GaN/N—ZnOheterojunction described in claim 5 is characterized by: In Step (1),the temperature for high-temperature reaction is 1,000-1,100° C., andthe reaction time is 90-180 minutes.
 7. The preparation method of abidirectional UV LED based on N—ZnON—GaN/N—ZnO heterojunction describedin claim 5 is characterized by: In Step (3), the metal plating method ismagnetron sputtering, thermal evaporation or electron beam evaporation,and the plating thickness is 20-60 nm.